Tokyo, Japan – Researchers from Tokyo Metropolitan University have come up with a new way to roll atomically thin sheets of atoms into “nanorolls”. Their unique approach uses transition metal dichalcogenide sheets with a different composition on either side, realizing a tight coil that yields coils up to five nanometers in diameter at the center and micrometers in length. Control over the nanostructure in these coils promises new developments in catalytic and photovoltaic devices.
Nanotechnology is giving us new tools to control the structure of materials at the nanoscale, promising a whole array of nano-tools for engineers to create next-generation materials and devices. At the forefront of this movement, a team led by Associate Professor Yasumitsu Miyata of Tokyo Metropolitan University has been studying ways to control the structure of transition metal dichalcogenides (TMDCs), a class of compounds with a wide range of interesting properties, such as flexibility. , superconductivity and unique optical absorption.
In their latest work, they set their sights on new ways to make nanorolls, nanosheets wrapped into tight roll-like structures. This is an attractive approach to making multi-walled structures: since the structure of each sheet is the same, the orientations of the individual layers are related to each other. However, the two existing ways to make nanoscrolls have significant problems. In one, the removal of sulfur atoms from the surface of the nanosheet creates distortions that cause the sheet to rotate; but in doing so, they destroy the crystalline structure of the sheet. On the other hand, a solvent is inserted between the nanosheet and the substrate, releasing the sheet from the substrate and allowing the formation of defect-free nanorolls. However, tubular structures made like this tend to have large diameters.
Instead of approaches like this, the team has come up with a new way to make the sheets stack. Starting with a single-layer molybdenum selenide nanosheet, they treated the nanosheet with a plasma and replaced the selenium atoms on one side with sulfur; such structures are called Janus nanosheets, after the ancient two-faced god. Gentle addition of a solvent then loosens the sheets from the base, which then spontaneously spin into rolls due to the asymmetry between the sides. These new nanoscrolls are many microns in length, significantly longer than previously produced single-walled TMDC nanosheets. Furthermore, they were found to be more tightly coiled than ever before, with a center up to five nanometers in diameter, meeting theoretical expectations. The spinnerets were also found to interact strongly with polarized light and have hydrogen-producing properties.
With unprecedented control over the nanostructure, the team’s new method forms the foundation for studying new applications of TMDC nanoscrolls for catalysis and photovoltaic devices.
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Janus Monolayer Transition Metal Dichalcogenide Nanorotations
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